Bugs in the freezer: Detecting faults in supermarket refrigeration systems using energy signals

Refrigeration is a major component of supermarket energy consumption. Ensuring faultless operation of refrigeration systems is essential from both economic and sustainability perspectives. Present day industry practises of monitoring refrigeration systems to detect operational anomalies have several drawbacks: (i) Over-dependence on human skills; (ii) Limited help in identifying the root-cause of the anomaly; and (iii) Presumption about high degree of instrumentation - which prevents their usage in supermarkets in developing economies. Existing approaches in literature to detect anomalies in refrigeration systems either are done in controlled laboratory settings or assume the availability of sensory information other than energy. In this paper, we present an approach to detect anomalous behavior in the operation of refrigeration systems by monitoring their energy signals alone. We test the performance of our approach using data collected from refrigeration systems across 25 stores of a real world supermarket chain. We find that using energy signal, we can not only detect anomalies but also narrow down the possible root-cause of the anomaly to a reduced set. Further, using energy signal along with data collected from other sensors (if available) allows us to reduce the false positive rate while identifying the root-cause of the anomaly.